Internal grinding machine

ABSTRACT

An internal grinding machine comprising a bed upon which is slidably mounted a work head containing a workpiece to be ground and a table which in turn slidably supports a grinding wheel head which houses a grinding wheel. The axes of the workpiece and the grinding wheel are parallel to one another and the work head and the grinding wheel head are slidable in directions transverse to such axes while the table is reciprocable in directions parallel to such axes. A dressing tool is pivotably mounted upon the bed so as to be pivotable within a plane perpendicular to the axes. A plurality of feeding means and control means for controlling the feeding means are provided for selectively and sequentially operating the grinding wheel head and table, as well as the work head and dressing tool whereby the workpiece may be moved toward and away from the grinding wheel, and the grinding wheel may be inserted within and withdrawn from the inner bore of the workpiece and also moved toward and away from the dressing tool, the latter in turn being pivotable toward and away from the dressing station.

United States Patent Kikuchi et al.

INTERNAL GRINDING MACHINE Inventors: Makoto Kikuchi, Kariya; Hiroaki Asano, Chiryu; Ikuo Otsu, Toyoda; Toyoaki Saeki, Kariya, all of Japan Toyoda Koki Kahushiki Kaisha, Kariya-shi, Japan Filed: Dec. 29, 1972 Appl. No.: 319,760

Assignee:

Foreign Application Priority Data Feb. 10, 1972 Japan 47-14647 U.S. Cl. 51/5 D, 5l/l65.87 Int. Cl B24b 53/00 Field of Search 51/l65.87, 165.93, 165 R,

11/1955 5l/l65.87 12/1971 Asano 5l/l65.87

Primary ExaminerAl Lawrence Smith Assistant ExaminerHarold P. Smith, Jr.

Attorney, Agent, or FirmOblon, Fisher, Spivak, Mc- Clelland & Maier [57] ABSTRACT An internal grinding machine comprising a bed upon which is slidably mounted a work head containing a workpiece to be ground and a table which in turn slidably supports a grinding wheel head which houses a grinding wheel. The axes of the workpiece and the grinding wheel are parallel to one another and the work head and the grinding wheel head are slidable in directions transverse to such axes while the table is reciprocable in directions parallel to such axes. A dressing tool is pivotably mounted upon the bed so as to be pivotable within a plane perpendicular to the axes. A plurality of feeding means and control means for controlling the feeding means are provided for selectively and sequentially operating the grinding wheel head and table, as well as the work head and dressing tool whereby the workpiece may be moved toward and away from the grinding wheel, and the grinding wheel may be inserted within and withdrawn from the inner bore of the workpiece and also moved toward and away from the dressing tool, the latter in turn being pivotable toward and away'from the dressing station.

10 Claims, 4 Drawing Figures PRIOR ART PATENTED MAY 2 8 I874 SHEU 2 OF 3 1 INTERNAL GRINDING MACHINE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to an internal grinding machine and more particularly to an improved internal grinding machine in which a dressing operation upon a grinding wheel does not affect the degree of grinding accuracy due to the fact that the grinding wheel and workpiece are always properly aligned with a dressing tool.

2. Description of the Prior Art One type of conventional grinding machine has the structure shown in FIG. I, and upon which the following grinding cycles are performed. A grinding wheel 3 is inserted within the inner bore of the workpiece W and subsequently, the workpiece W is advanced toward the grinding wheel 3. When a rough grinding operation is completed, the advancement of the workpiece W is temporarily stopped at the middle stop position as shown by the full lines in FIG. 1. At this time, the grinding wheel 3 is withdrawn from the inner bore of the workpiece W and is subsequently dressed by the dressing means 13 fixed upon the work bed 8 whereby the diameter of the grinding wheel 3 is decreased through an amount Al, the resulting diameter being shown by the phantom line 3a.

After the dressing operation, the grinding wheel 3 is inserted again within the inner bore of the workpiece W. The relative position of the workpiece W is compensated by the amount AI and consequently, a fine grinding operation may be performed by advancing the workpiece W toward the grinding wheel 3.

As stated above, in such conventional internal grinding machines, the amount of dressing is dependent upon the middle stop position, and the position of the workpiece W is compensated through the distance equal to the amount of dressing and the final dead stop position of the workpiece. W is also controlled in accordance with the middle stop position. Accordingly, such machines have the disadvantage that the finishing accuracy is directly affected by any deviation in the middle stop position as well as the accuracy of compensation.

Furthermore, if an additional dressing operation is required after the fine grinding operation is completed in order to grind workpieces of hard-to-grind material or in order to obtain a certain degree of accuracy, the

dressing amount Al is unnecessarily increased, whereby the diameter of the grinding wheel 3 rapidly decreases, because the dressing amount is equal to the grinding depth after the first dressing operation.

SUMMARY OF THE INVENTION The axes of the workpiece and the grinding wheel are parallel to one another and the work head and the grinding wheel head are slidable in directions transverse to such axes while the table is reciprocable in directions parallel to such axes. A dressing tool is pivotably mounted upon the bed so as to be pivotable within a plane perpendicular to the axes. A plurality of feeding means and control means for controlling the feeding means are provided for selectively and sequentially op erating the grinding wheel head and table, as well as the work head and dressing tool whereby the workpiece may be moved toward and away from the grinding wheel, and the grinding wheel may be inserted within and withdrawn from the inner bore of the workpiece and also moved toward and away from the dressing tool, the latter in turn being pivotable toward and away from the dressing station.

BRIEF DESCRIPTION OF THE DRAWINGS Various other objects, features and attendant advan-' tages of the present invention will be more fully appreciated as the same becomes better understood from the following detailed description when considered in connection with the accompanying drawings, in which like reference characters designate like or corresponding parts throughout the several views, and wherein:

FIG. 1 is a schematic view of the main parts of a conventional interal grinding machine, illustrating the principles involved in connection with the grinding opera- DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawings, and more particularly to FIGS. 2 and 3 thereof, a bed 1 supports a grinding wheel head 2 which mounts a grinding wheel 3, the grinding wheel head 2 being mounted upon bed I through means of a table 4. The grinding wheel head 2 and the table 4 are respectively mounted so as to slide relative tov bed 1 and in directions transverse to eachother. More particularly, the table 4 slides upon the bed I in a direction parallel to the grinding wheel axis, through reciprocating means described hereinbelow in detail, while the grinding wheel head 2 slides upon table 4 in a direction perpendicular to the grinding wheel axis, through feeding means also described hereinbelow in detail.

A motor 5 rotates the grinding wheel 3 which is fixed upon a grinding wheel shaft 7 which is rotatably mounted upon the grinding wheel head 2, the rotational drive of the motor being transmitted to the grinding wheel shaft 7 by means of pulley belts 6. A work head 8 is also slidably mounted upon the bed 1 so as to movably support the workpiece W. The work head 8 ing wheel axis through other feeding means so as to enable the grinding operation to be performed upon the workpiece W, the feeding means being described in detail hereinafter. A motor 9 rotates a chuck 11 which is mounted upon a spindle which is, in turn, rotatably carried upon the work head 8, the rotation of motor 9 being transmitted to the spindle 10 through a set of belts 12.

A dressing tool 13 is provided for dressing the grinding wheel 3, and is fitted upon a pivotable arm 14 which is supported upon the bed 1. The arm 14 is moved to the lowered or dressing position in order to perform the dressing operation upon the grinding wheel 3. After completion of the dressing operation, arm 14 is rotated to the raised position by pivoting means described in detail hereinafter, whereby the dressing tool 13 is maintained out of the normal dressing position.

Referring now to FIG. 4, the feeding means for the work head 8, the reciprocating means for the table 4 and the feeding means for the grinding wheel head 2, and the rotating device for the arm 14 and dressing tool 13 of the internal grinding machine are illustrated. With respect to the reciprocating means for table 4, a cylinder 15 is equipped with a slidable piston 16, the piston rod 17 of the piston 16 being connected to the table 4 so as to reciprocate the same. Mounted upon the side of the table 4 is a dog mounting plate upon which a plurality of dogs D, D are mounted in a longitudinally spaced relationship relative to each other. The required reciprocating movement of the table 4 is provided by means of the dogs and an appropriate control circuit described in detail hereinafter, the dogs D and D serving to actuate a switch lever 18 which is pivotable around a pivot pin 19, the rotary motion of the switch lever 18 being in turn transmitted to the table direction switching valve V.,.

For example, when the switch'lever 18 is rotated in a clockwise direction as viewed in FIG. 4, the switching valve V, is switched to its b port whereby a pilot pressure is supplied to another switching valve V so as to switch the same to its respective b port. As a result, hydraulic fluid is fed to the rear chamber of the cylinder 15 whereby the table 4 initiates its advancing move ment. On the contrary, when the switch lever 18'is rotated in a counter-clockwise direction as viewed in F IG. 4, the switching valve V is'switched to its a port, and the switching valve V is also switched to its a port able lever 20 which is controlled by means of the switch lever 18 and a tension spring 20a.

Still further, a cylinder 22 is provided with a piston 24 for clamping the switch lever 18. Piston 24 is slidably mounted within cylinder 22 and is urged in one direction by means of a compressed spring 25. A clamping pawl 28, clutched to a pin 27 upon the switch lever 18, is mounted to the piston rod 26 which is of course connected to the piston 24. Accordingly, when hydrauby the pilot pressure supplied from the valve V As a result, the hydraulic fluid'is now supplied to the forward chamber of the cylinderv 15 whereby the table 4 is moved rearwardly, A manual-automatic switching valve V is also provided so that the operation can be changed from a manual to an automatic mode, and vice versa.

A lifting plate 21 is provided for lifting the dog D so that the dog D does not engage the switch lever 18 when the .table 4 is being returned to the original position thereof. The lifting plate 21 is associated with a switching valve V through means of a rod 23. When for example, the switch valve V is switched to its a port, the lifting plate 21 is lifted by means of the rod 23. On the contrary, when the switching valve V is switched to its b port, the lifting plate 21 moves downwardly under the force of gravity. Another switching valve V is provided for moving the table in-cooperation with the switching valve V The switching valve V is operably connected to the switching valve .V, through a pivothe fluid is not fed to the cylinder 22 and no grinding operation is required, the piston 24 is returned by the spring 25, the pin 27 is pulled toward the right by means of the clamping pawl 28 and the switch lever 18 is rotated in a counterclockwise direction as viewed in FIG. 4, whereby the switching valve V, is switched to its a portsov that the table 4 is never able to be advanced accidentally, a safety system thus being provided.

Still referring to FIG. 4, atable velocity switching valve V is also disposed 'within the control circuitry, and when the valve V is switched to its b port, the exhaust hydraulic oil from the cylinder 15 is exhausted through the b port of the switching valve V and the a port of another switching valve V to a reservoir tank T, so that the table 4 is advanced or moved toward the left at a high velocity. When the grinding wheel3 approaches within the vicinity of the workpieceW, the dog D actuates .the operating rod 29 whereby the switching valve V is switched to its a port so that the exhaust oil from the cylinder 15 is exhausted through the a port of the switching valve V and throttle valve 30 to thetank T whereby the table4 is advanced at a slow velocity as determined by throttle valve 30. Another throttle valve 31 is provided within the bypass passage of the switching valve V in order to prevent the stoppage of the table 4 when the switching valve V vis switched from it's'b port to its a port.

A throttle valve 32 is provided for a hydraulic biasing effect with respect to cylinder 15, while check valves 33-36 are respectively associated within the circuitry in conjunction with the various switching valves. A limit switch LS1 is mounted upon the bed 1 and may be actuated by means of the dog D when the table 4 is; returned to its original position. Similarly, another limit switch LS2 is also mounted upon the bed 1 to be actuated-by means of the dog B, when the table 4 is returned to the position at which the dressing operation upon the grinding wheel is completed. Still another limit switch LS 3 is mounted upon the bed-l and is continuously activated by means of dog D during the grinding operation performed upon workpiece W.

With respect to the feeding means for the grinding wheel head 2, a dressing cylinder 37 is provided for advancing the grinding wheel head 2 and the grinding wheel 3 toward the dressing tool l3'to permit the tool 13 to perform the dressing operation. Movement of the piston 38 disposed within the cylinder 37 is transmitted through a conventional ratchet mechanism to a threaded shaft 39 which is threadingly engaged with a support nut 40mounted upon the lower surface of the grinding wheel head 2 whereby the grindingwheel 3 is advanced by rotation of shaft 39. The ratchet mechanism comprises a pinion 42 meshingly engaged with a rack disposed upon the piston rod 41, a ratchet pawl 44 mounted upon a pivotable plate 43 and being movable together with the pinion 42,'and a ratchet wheel 45'eng'ageable with the ratchet pawl 44. The distance fed by the ratchet can be easily controlled by controlling the angular position of the plate 43. A switching valve V is provided for controlling the amount of hydraulic fluid supplied to and exhausted from the cylinder 37.

Turning now to'the feeding means for the work head 8, a cylinder 46 has a piston 47 which is slidably mounted therein, there being a rack formed upon the piston rod 48 of the piston 47 for engagement with a pinion 49 which is connected through the gears 50, 51

4 and 52 to a threaded shaft 53. The shaft 53 is threadingly engaged with a nut 54 which is mounted upon the lower surface of the work head 8 whereby the work head 8 is moved through the rotation of shaft 53 relative to nut 54. A dog plate 55 is equipped with a dog D, for activating a limit switch LS4 for confirming the original position of the work head 8, while another dog D actuates another limit switch LS 5 so as to confirm the middle stop position. A switching valve V is provided for switching the direction in which the piston 47 is moved, while another switching valve V serves to return the piston 47 a predetermined distance after it has reached the middle stop position.

A return distance control cylinder 56 is associated with valve V for controlling the distance that the work head 8 is returned. A piston 57 is slidably mounted within the control cylinder 56, and when hydraulic oil is supplied to the rear chamber of the cylinder 56 by switching the switching valve V to its a port, the piston 57 is moved toward the left whereby the hydraulic fluid exhausted from the forward chamber of the cylinder 56 is directly supplied to the forward chamber of cylinder 46 whereupon the piston 47 is returned a predetermined distance. An adjusting screw 58 is disposed rearwardly of piston 57, and a compressed spring 59 for biasing the piston 57 toward the left is disposed about screw 58. A throttle valve 60 controls the feed velocity of the fine grinding operation while another throttle valve 61 controls the feed velocity for the rough grinding operation, a switching valve V being disposed therebetween. Various check valves 62-65 are also associated with cylinders 46 and 56. A dog D is mounted upon the piston rod 48 for actuating a limit switch LS 6 which confirms the end of the forward movement of the piston rod 48.

Turning now to the rotating device for the pivotable arm 14 and the dressing tool 13, an arm operating cylinder 66 has a piston 67 slidably mounted therein, a rack being formed upon the piston rod 68 of the piston 67 for engagement with a pinion 69 which is connected to the rotatable arm 14, whereby movement of the piston is transmitted to the arm 14. A switching valve V controls the supply of hydraulic fluid to the arm operating cylinder 66. Consequently, when the switching valve V is switched to its a port, another switching valve V, is switched to its b port .by the pilot pressure of valve V whereby the hydraulic oil exhausted from the cylinder 15 is conducted through a dressing velocity setting throttle valve 80 to the tank T so that the table 4 is moved at the dressing velocity. A stopper 7] is provided for limiting the movement of the rotating arm 14, while av compression spring 72 and a throttle valve 73 resiliently and hydraulically bias piston 67, respectively. i

As is clear from the above-described structure, the internal grinding machine of the present invention automatically and continuously performs the grinding cycle characteristic of an internal grinding operation, that is, the reciprocating movement of the table 4, the feeding of the workpiece mounted upon the work head 8, and the feeding of the grinding wheel 3 mounted upon the grinding wheel head 2. A complete grinding cycle of an internal grinding machine as illustrated will now be described, with particular reference to FIGS. 2 and 4.

. As shown in FIG. 4, the table 4, the grinding wheel head 2, and the work head 8 are in their original positions, respectively. The switch lever 18 is maintained in the position shown by means of the cylinder 22 while the lifting plate 21 is maintained in its raised position by means of rod 23 so that the dog D is raised whereby it does not actuatethe switch lever 18 in a clockwise direction when the table 4 is being retracted. The manual-automatic switching valve V, has been manually switched to its a port, and in such condition, the actuating button is pushed so as to actuate the solenoid SOL l and thus the valve V, is switched to its a port.

Hydraulic oil is thus supplied to the cylinder 22, whereby'the clamping pawl 28 is moved toward the left against the biasing action ofthe spring 25 and the clutch or lock mechanism of the pin 27 of the switch lever 18 is released so as to permit free movement of the switch lever 18. The hydraulic oil also passes through the a port of the valve V so as to switch the valve V to its b port. The valve V5 however, is not switched, and the lifting plate 21 is still at the raised position as long as the valve V is not switched to its b port, since the pilot pressure applied to the left side of the valve V is not decreased by the check valve 34. When however, the valve V is switched to its b port, the pivotable lever 20 is rotated in a counterclockwise direction whereby the switch lever 18 is rotated in a clockwise direction around the pivot pin 19 and simultaneously therewith the switching valve V, is switched to its b port. Accordingly, the hydraulic oil'fro'm the valve V is supplied through the b port of the switching valve V so as to actuate the valve V due to the pilot pressure thereof and thereby switch the same to its b port. The hydraulic oil is thus supplied through the b port of the valve V and the 17 port of the valve V as well as the check valve 33 to the cylinder 15 so that the table 4 initiates quick advancing movement.

At the time of initiation of the quick advancing movement of the table 4, the valve V is switched to its b port, whereby the actuating rod 23 associated with the valve V is moved downwardly-so as to lower the dog D The pilot pressure is then transmitted to the left side of the valve V when the valve V is switched to its b port, whereupon the valve V is switched to its a port whereby the rotatable lever 20 is returned in a clockwise direction by means of the spring 20a so as to permit the free rotation of the switch lever 18. The table 4 is thus quickly advanced and when the grinding wheel 3 is moved to within the vicinity of the workpiece W which is held by means of the electromagnetic chuck 11, the dog D actuates the limit switch LS 3 while the dog D actuates the rod 29 of valve V for a slow feed run. The valve V is switched to its a port and accordingly the exhaust oil from the cylinder l5 is passed through the b port of the valve V the a port of the valve V the a port of the valve V and through the throttle valve 30 so as to return to the tank T. Accordingly, the advance feeding velocity of the table 4 is switched to a slower velocity and the grinding wheel 3 is inserted within the inner bore of the workpiece W.

When the grinding wheel 3 is advanced at a slow feeding speed, the dog D rotates the switch lever 18 in a counterclockwise direction so as to switch the switching valve V to its a port. The valve V is also switched to its a port by means of the pilot pressure, and the hydraulic oil is supplied to the forward chamber of the cylinder so as to retract the table 4. During retraction of table 4, the exhaust oil from the rear chamber of the cylinder 15 is passed through the a port of the valve V the a port of the valve V and the throttle valve so as to return to the tank T whereby the table 4 is retracted in the slow mode. Whenthe front end of Y the slowly retracting grinding wheel 3 reaches the end of the workpiece W, the switch lever 18 is rotated in a clockwise direction by means of the dog D -,'because the lifting plate 21 has been moved to its lowered position,

the dog D dropping downwardly under the influence initiated, the solenoid SOL 5 is actuated so as to switch,

the switching valve V to its a port, whereby the hydraulic oil is supplied to the rear chamber of the cylinder 46 through the b port of the switching valve V and the check valve 63. The exhaust oil from the forward chamber of the cylinder 46 is passed through the throttle valve 61 for controlling the rough grinding feed velocity, the a port of the valve V and the return control cylinder 56 to the tank T whereupon the piston 47 is advanced. The advancement of piston 47 is in turn transmitted through the rack pinion gears 50,51, and 52 to the shaft 53 whereupon the work head 8 is advanced so as to provide for the rough grinding operation upon the workpiece W.

When the workpiece W is advanced to the position shown by the full lines in F IG. 2, that is, when the rough grinding operation is completed, thedog D actuates the limit switch LS 5 which confirms the completion of the rough grinding operation. The solenoid SOL 4 is in turn actuated by a signal from the limit switch LS 5 so as to switch the switching valve V to its a port. The hydraulic oil is then supplied to the rear chamber of the return control cylinder 56 whereupon the piston 57 is moved toward the left. The exhaust oil from the forward chamber of the cylinder 56 is supplied directly to the forward chamber of the feed cylinder 46 so that the piston 47 is retracted to the right as viewed in FIG. 4, I corresponding to the supply of the oil, whereby the. work head 8 is retracted a predetermined distance. In

conjunction with this operation, the. solenoid SOL 3 is actuated by another signal from the limit switch LS5, and consequently, the valve V is switched to its a port whereby hydraulic oil is supplied to the rear chamber of the dressing cylinder 37 so as to advance the piston 38. The advance movement of piston 38 is transmitted, by means of the ratchet mechanism, to shaft 39 for. a predetermined distance set byv the plate 43 whereby the the full line 3 in FIG. 2 to the position shown by the phantom line 3a, that is, toward the dressing tool 13.

In addition, the solenoid SOL l is de-activated by still another signal from the limit switch LS 5 whereby the valve V, is switched to the b port, the valve V is switched to the a port by means of the pilot pressure applied to the left side thereof from the b port of the valve V hydraulic fluid thus passing through the check valve 34 so as to raise the lifting plate 21 by means of the rod 23. Accordingly, when the table 4 is retracted, the dog D does not contact the switch lever 18 and passes the same because the dog D, has been raised to its elevated position by means of the lifting plate 21.

The table 4 and the grinding wheel 3 are retracted until the wheel 3 reaches the position shown in the phantom line 3b of FIG. 2. Subsequently, the dog D', is disengaged from the limit switch LS 3 and the dog D is similarly disengaged from the rod-29 of the valve V so as to permit switching of the same to the b port. The solenoid SOL 2 of the valve V is then actuated by a signal from the limit switch LS 3 so as to switch the same to the a port, and when this is accomplished, the valve V is'switched to the b port by means of the pilot pressure supplied from the valve V and in this manner, the exhaust oil from the cylinder 15 is passed through the throttle valve 80 to the tank T so that the table 4 is moved at the dressing feed velocity.

In conjunction with the velocitychange of the table 4', hydraulic oil is supplied to the dressing cylinder 66 whereby the piston 67 is advanced so'as to rotate the arm 14 through means of the rack of the piston rod 68 and the pinion 69 of the pivot arm 14, whereby the dressing tool 13 is brought to the dressing position wherein the tool 13 contacts the grinding wheel 3. When the table 4 is retracted at the dress feed velocity, the dressing operation is performed upon the grinding wheel 3 by dressing tool 13 and thus, the diameter thereof is decreased by an amount I so that the resulting diameteris that shown in the phantom line 3c of FIG. 2. .r

As stated above, the lifting plate 21 is still maintained in its raised position, and the table 4 is continuously retracted at the dress feed velocity, because the dog D is not able to rotate the switch lever 18 in a clockwise direction and the switchingvalve V is still switchedto its a port which provides for the retracting motion of table 4. The dog D will subsequently actuate the limit switch LS 2 to confirm that the table 4 is located at a position which corresponds to the end of the dressing operation, and when the limit switch LS 2 is actuated, the solenoid SOL l of valve V is actuated to switch valve V, to its a port whereby the valves V and V; are

respectively switched to their b ports in the above mentioned manner. Accordingly, the switch lever 18 is rotated in a clockwise direction by means of the lever 20, and the table 4 is actuated so as to advance, the rod 23 and the lifting plate 21' being lowered. The grinding wheel 3 is then dressed by the dressing tool 1-3 through the advancement movement of the table 4 .to within the vicinity of the workpieceW, and thus the limit switch LS 3 is-actuated by means of the dog D and the valve V is switched to its a port by means of the dog D, so

grinding wheel 3 is advanced from the piston shown by that the grinding feed velocity isren'de'red to the table. The solenoid SOL 20f the valve V is simultaneously de-activated by means of a signal from the limit switch LS 3 and accordingly the valve V, is switched to the b port and the valve" V is switched to the a port by the pilot pressure supplied from the valve V whereby the piston 67 of the cylinder 66 is returned by the spring 72 and the arm 14 is rotated to its raised position.

The dressed grinding wheel 3 is now inserted within the workpiece W and the reciprocating movement of table 4 is initiated by actuating the switch lever 18 by means of the dogs D and D in a manner similar to that employed during the rough grinding operation. When the reciprocating movement is initiated, the solenoids SOL 4 and SOL 6 are respectively activated and deactivated so as to switch the valves V and V to the 12 ports whereby the hydraulic oil is supplied to the rear chamber of the cylinder 46. Most of the exhaust oil is supplied to the forward chamber of the return distance control cylinder 56 while a portion of the exhaust oil is exhausted through the throttle valve 60, the check valve 65 and the rear chamber of the cylinder 56 to the tank T. Thus, the piston 47 is advanced, and the advancing movement thereof is transmitted to the shaft 53, whereby the work head 8 is advanced at the fine grinding feed velocity. When the fine grinding operation upon the workpiece W is completed, the dog D upon the piston rod 48 activates the limit switch LS 6 which confirms completion of the operation. After actuation of the limit switch LS 6, a timer is actuated and a spark out grinding operation is performed upon the workpiece W.

The solenoid SOL 5 is then de-activated so as to switch the valve V to the b port by means of a signal which is issued after a predetermined time, whereby the hydraulic oil is supplied to the forward chamber of the cylinder 46 and the exhaust oil from the cylinder 46 is exhausted to the tank T, the piston 47 thus being retracted, the movement of piston 47 being transmitted to the work head 8 so as to return the same to its original position. The limit switch LS4 for confirming the original position of head 8 is actuated by means of the dog D whereby the return of the work head 8 is in fact confirmed and may await the next cycle.

After the passage of the designated time period set by the timer, the solenoid SOL l is de-activated and the valve V, is switched to the b port. The lifting plate 21 is then raised as in the dressing cycle, and the pin 27 is pulled by means of the clamping pawl 28 of the cylinder 22, whereby the switch lever 18 is rotated in a counterclockwise direction. Thetable 4 is retracted and the dog D, isdisengaged from the limit switch LS 3, and when the grinding wheel 3 is withdrawn from the workpiece W, the dog D is disengaged from the rod 29 of the valve V, so as to retract the table 4 at a rapid velocity. During retraction, the dog D is not in contact with the switch lever 18 because of the raised position of the lifting plate 21, and consequently, the table 4 reaches its original position. The dog D actuates the limit switch SL 1, whereby the return of the table 4 is confirmed to await the next cycle. At the rear end'of the table 4, no impact is generated as the throttle valve 32 serves to hydraulically bias the rearward movement of the table. 7

It is thus apparent that during the grinding cylce of the conventional apparatus, one middle stop position of the work head and one dressing operation are provided. However, with the internal grinding machine of the present invention, the relative position between the dressing tool and the grinding surface of the grindingv wheel and the finished surface of the workpiece are not changed by the dressing operation and are always aligned with each other. Accordingly, it is possible to dress the grinding wheel to obtain a high degree of accuracy and the finish surface required, by providing a plurality of the limit switches upon the plate so as to stop the work head 8 at a plurality of intermediate stops.

As is clear from the above description, the finish surface of the workpiece W and the grinding surface of the grinding wheel 3 are always coincided with the edge of the dressing tool 13 regardless of the dressing operation upon the grinding wheel 3 and the middle stop of the work head 8 since the dressing operation is performed by advancing the grinding wheel 3 toward the dressing tool 13 and the grinding operation is in turn performed by advancing the workpiece W toward the grinding wheel 13. Accordingly, there is no disadvantage that the finishing accuracy upon the workpiece is affected by the accuracy of the middle stop position of the work head or the number of the dressing operations which is limited as in conventional machines. In accordance with the present invention, the advantages of high accuracy and an efficient grinding operation can be attained.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. it is to be understood therefore, that within the scope of the appended claims the present invention may be practiced otherwise than as specifically described herein.

We claim:

1. An internal grinding machine comprising:

a bed;

a table slidably mounted upon said bed;

a grinding wheel head slidably mounted upon said table and rotatably carrying a grinding wheel;

a work head slidably mounted upon said bed for rotatably supporting a workpiece which is rotatable around an axis which is parallel to the axis of said grinding wheel;

a dressing tool mounted upon a pivotable arm which is mounted upon said bed and pivotable in a plane perpendicular to said axis of said grinding wheel;

first feed means operably connected to said grinding wheel head for moving said grinding wheel toward said dressing tool;

a second feed means operably connected to said work head for moving said workpiece toward and away from said grinding wheel;

third feed means for producing relative movement between said work head and said table in a direction parallel to said axis of said grinding wheel;

fourth feed means for pivotably moving said pivotable arm toward and away from a dressing position;

first control means for stopping the feed motion of said second feed means and for actuating said first feed means so as to advance said grinding wheel toward said dressing tool; and

second control means-for controlling the movement of said third feed means relative to said first and second feed means. a

2. An internal grinding machine as set forth in claim 1, wherein said first control means comprises:

a first detecting means associated with said second feed means and capable of generating a signal when said work head has been moved' toward said a first valve means connected to said second feed means for controlling hydraulic fluid supplied to second valve means provided between said first 7. An internal grinding machine as set forth in claim 6, wherein said first control valve means comprises:

a third valve means having two positions and connected to a reservoir tank and said third feed said second feed means; and means for selectively supplying said fluid to said -a second valve means providedbetween said first third feed means; and I valve means and Said econd fee m n an a fourth valve means having two positions and operasponsive Said first detecting means for retracting bly connected to said third valve means and said sa d work head en said s g is g n e y first switching lever for controlling said third valve sald first detect ng fl m means in accordance with the position of said 3. An mtemal grinding machine as set forth in Claim i hi l Where!" 531d. first control mefins P" 8. An internal grinding machine as set forth in claim a first detecting means associated with said second 6, wherein i second comm] means f th feed means and capable of generating a signal prises; I 1 p when said work head has been moved toward said IS a second vswitching lever pivotably mounted upon workplace through a predeterminefj dlstancefio as said bed and engageable with said first switching to thereby complete a rough grmdmgoperatron; lever; first valve means connected to said second feed a clamping means engageable with said first switchmeans for COIltl'Ollll'lgllYdI'flUllC fluid supplied to ing levenam v said Second feed means; second control valve means for controlling said clamping means so as to rotate said first switching valve means and said second feed means and responsive to said first detecting means for retractingsaid work head when said signal is generated by said first detecting means; and 1 a control cylinder means controlled by said second valve means for retracting said work head through a predetermined distance by supplying a predetermined amount of said fluid to said second feed means. v

4. An internal grinding machine as set forth in claim 3, which further comprises:

a first check valve means for passing said fluid in only one direction from said first valve means to said second feed means; and I a second check valve means for passing said fluid in only one direction from said second feed means to said control cylinder means. 7

5. An internal grinding machine as set forth in claim 2, wherein said first feed means comprises: 4

a switching valve and a hydraulic cylinder controlled by said switching valve, said switching valve being responsive to said signal generated by said first detecting means so as to advance said grinding wheel head toward said dressing 'tool.

6. An internal grinding machine as set forth in claim 1, wherein said second control means comprises;

first control valve means for selectively supplying hydraulic fluid to said third feed means;

a first switching lever pivotably mounted upon said bed and connected 'to said first control valve means; v r

first dog 'means mounted upon said table and engageable with said firstswitching lever, said first dog means being operable so as to rotate said first switching lever in a first direction so as to change I the direction of motion of said third feed means; and

second dog means'm'ounted upon said table and engageable with said first switching lever, said second 0 dog means being operable so asto rotate said first switching lever in a second direction 'so as to change the direction of motion of said third feed means.

lever in said first direction while said second switching lever is disengaged from said first switching lever means and for controlling said second switching lever so as to rotate said first switching lever in said second direction while said clam'ping means is disengaged from said first switching lever.

9. An internal grinding machine as set forth in claim 8, which further comprises:

a lifting means operably connected to said second means so as to prevent the engagement between said first switching lever and said second dog means. g 10. An internal grinding machine as set forth in claim 5, which further comprises:

1 second detecting means for generating a signal when said grinding wheel has reached one end of its stroke for a dressing operation; and

wherein said second control means comprises first control valve means for selectively supplying said fluid to said third feed means, a first switching lever pivotably mounted upon said'bed and connected to said first control valve means, first and second dog rotating said first'switching lever, a second switching lever pivotably mounted'upon said bed and en- 50 gageable with said first switching lever, a clamping ond dog means so as to prevent engagement between said first switching lever and said second dog means, and second control valvefmeans for controlling said firstcontrol valve means'through said second switching lever and for controlling said lifting means, said second control valve means being capable of rotating said first switching lever in one direction when said first detecting meansgenerates said signal and rotating said first switching lever in another direction when a second detecting means generates another signal.

control valve means for lifting said second dog means mounted upon said table for alternatively means engageable with and controlling said first switching lever, a lifting means for lifting said sec-, 

1. An internal grinding mAchine comprising: a bed; a table slidably mounted upon said bed; a grinding wheel head slidably mounted upon said table and rotatably carrying a grinding wheel; a work head slidably mounted upon said bed for rotatably supporting a workpiece which is rotatable around an axis which is parallel to the axis of said grinding wheel; a dressing tool mounted upon a pivotable arm which is mounted upon said bed and pivotable in a plane perpendicular to said axis of said grinding wheel; first feed means operably connected to said grinding wheel head for moving said grinding wheel toward said dressing tool; a second feed means operably connected to said work head for moving said workpiece toward and away from said grinding wheel; third feed means for producing relative movement between said work head and said table in a direction parallel to said axis of said grinding wheel; fourth feed means for pivotably moving said pivotable arm toward and away from a dressing position; first control means for stopping the feed motion of said second feed means and for actuating said first feed means so as to advance said grinding wheel toward said dressing tool; and second control means for controlling the movement of said third feed means relative to said first and second feed means.
 2. An internal grinding machine as set forth in claim 1, wherein said first control means comprises: a first detecting means associated with said second feed means and capable of generating a signal when said work head has been moved toward said workpiece through a predetermined distance so as to thereby complete a rough grinding operation; a first valve means connected to said second feed means for controlling hydraulic fluid supplied to said second feed means; and a second valve means provided between said first valve means and said second feed means and responsive to said first detecting means for retracting said work head when said signal is generated by said first detecting means.
 3. An internal grinding machine as set forth in Claim 1, wherein said first control means comprises: a first detecting means associated with said second feed means and capable of generating a signal when said work head has been moved toward said workpiece through a predetermined distance so as to thereby complete a rough grinding operation; a first valve means connected to said second feed means for controlling hydraulic fluid supplied to said second feed means; a second valve means provided between said first valve means and said second feed means and responsive to said first detecting means for retracting said work head when said signal is generated by said first detecting means; and a control cylinder means controlled by said second valve means for retracting said work head through a predetermined distance by supplying a predetermined amount of said fluid to said second feed means.
 4. An internal grinding machine as set forth in claim 3, which further comprises: a first check valve means for passing said fluid in only one direction from said first valve means to said second feed means; and a second check valve means for passing said fluid in only one direction from said second feed means to said control cylinder means.
 5. An internal grinding machine as set forth in claim 2, wherein said first feed means comprises: a switching valve and a hydraulic cylinder controlled by said switching valve, said switching valve being responsive to said signal generated by said first detecting means so as to advance said grinding wheel head toward said dressing tool.
 6. An internal grinding machine as set forth in claim 1, wherein said second control means comprises: first control valve means for selectively supplying hydraulic fluid to said third feed means; a first switching lever pivotably mounted upon said bed and connected to said first control valve means; first dog means mounted upon said table and engageable with said first switching lever, said first dog means being operable so as to rotate said first switching lever in a first direction so as to change the direction of motion of said third feed means; and second dog means mounted upon said table and engageable with said first switching lever, said second dog means being operable so as to rotate said first switching lever in a second direction so as to change the direction of motion of said third feed means.
 7. An internal grinding machine as set forth in claim 6, wherein said first control valve means comprises: a third valve means having two positions and connected to a reservoir tank and said third feed means for selectively supplying said fluid to said third feed means; and a fourth valve means having two positions and operably connected to said third valve means and said first switching lever for controlling said third valve means in accordance with the position of said switching lever.
 8. An internal grinding machine as set forth in claim 6, wherein said second control means further comprises: a second switching lever pivotably mounted upon said bed and engageable with said first switching lever; a clamping means engageable with said first switching lever; and second control valve means for controlling said clamping means so as to rotate said first switching lever in said first direction while said second switching lever is disengaged from said first switching lever means and for controlling said second switching lever so as to rotate said first switching lever in said second direction while said clamping means is disengaged from said first switching lever.
 9. An internal grinding machine as set forth in claim 8, which further comprises: a lifting means operably connected to said second control valve means for lifting said second dog means so as to prevent the engagement between said first switching lever and said second dog means.
 10. An internal grinding machine as set forth in claim 5, which further comprises: second detecting means for generating a signal when said grinding wheel has reached one end of its stroke for a dressing operation; and wherein said second control means comprises first control valve means for selectively supplying said fluid to said third feed means, a first switching lever pivotably mounted upon said bed and connected to said first control valve means, first and second dog means mounted upon said table for alternatively rotating said first switching lever, a second switching lever pivotably mounted upon said bed and engageable with said first switching lever, a clamping means engageable with and controlling said first switching lever, a lifting means for lifting said second dog means so as to prevent engagement between said first switching lever and said second dog means, and second control valve means for controlling said first control valve means through said second switching lever and for controlling said lifting means, said second control valve means being capable of rotating said first switching lever in one direction when said first detecting means generates said signal and rotating said first switching lever in another direction when a second detecting means generates another signal. 